No. 4.] 



TREE SURGERY. 



445 



Fig. 5. — Section of pine 

 log, showing depth to whicli 

 knots penetrate. 



"worm i the bud" being responsible for the failure of some ; 



others are destroyed by the .elements, others still hy bu'ds 



or other animals. As the young tree continues to grow, 



many of the 3'oung shoots die back. 



Here again insects take a prominent 



part in the pruning ; twig borers, 



twig pruners, plant lice, bugs and 



other insects attack the tender shoots 



or 3'oung foliage, and the tree is able 



to support only a few of the strongest 



shoots. The tree, in self-defence, is 



constantly attempting to produce 



more shoots than it can mature ; and 



there comes a competition among its 



members, the weaker being over- 

 shadowed and killed out by the 



stronger. If other trees of about the 



same age are growing thickly around 



our young tree, it must compete with them also ; for the tree 



which is outgrown and overshadowed by its fellows, lacking 



the life-giving light, must surely die. As a thicket of young 



trees grows rapidly upward, the 

 lower branches are shaded by 

 the tops, die, decay, and finally 

 fall to the o;i-ound, leavins' the 

 wounds to be healed as best 

 the}^ may. As the limbs are 

 usually small, and .rot or break 

 off close to the trunk, the 

 wounds heal readily. Still, in 

 many cases, especially those of 

 resinous coniferous trees, like 

 the white pine, a stump is left 

 which does not entirely decdy, 

 but after many years is finally 



covered by the annual wood growth of the trunk. This 



process is illustrated by Fig. 5. 



Such stumps, blackened, weather-stained, and perhaps 



partially decayed, are found in the trunks of most pines, 



Fig. 6. — Dead branches on pine 

 trunk, the origin of bkick knots in 

 the timber. 



